1. Field of the Invention
The present invention relates to an optical information recording medium and a method of manufacturing an optical information recording medium, and in particular to an optical information recording medium provided with a recording layer containing a dye and a photocured layer formed by photocuring a photocurable resin, and to a method of manufacturing the optical information recording medium.
2. Description of the Related Art
Conventional writable optical information recording media (optical disks), on which it is possible to record information a single time by laser light, are called CD-Rs and are well known. A representative structure of a CD-R type optical information recording medium is a structure in which a dye recording layer formed from an organic dye, a light reflecting layer formed from a metal such as gold, and a protective layer formed of resin, are layered in that order on a transparent, disk-shaped substrate. Recording of information onto the optical disk is carried out by irradiating near infrared laser light (usually laser light of a wavelength in a vicinity of 780 nm) onto the optical disk. The illuminated portions of the dye recording layer absorb the light such that the temperature at these portions rises. The optical characteristics of these portions change due to the physical or chemical change (e.g., the formation of pits or the like), whereby information is recorded. On the other hand, playback of information is usually carried out by irradiating, onto the optical disk, laser light of the same wavelength as that of the laser light used for recording, and detecting the differences in the reflectances of the regions (recorded regions) of the dye recording layer at which the optical characteristics have changed and the regions (unrecorded regions) at which the optical characteristics have not changed.
Recently, writable optical disks called DVD-Rs have been put into practice as media which enable recording at a higher density than CD-Rs, and as such are rising in rank as large-capacity recording media. DVD-Rs usually have a structure in which two disks, each formed by a dye recording layer formed from an organic dye, a light reflecting layer, and a protective layer layered in that order on a transparent disk-shaped substrate, are adhered together by an adhesive with their dye recording layers at the inner sides thereof. Alternatively, a DVD-R has a structure in which the aforementioned disk and a disk-shaped protective substrate of the same configuration are adhered together by an adhesive with the dye recording layer at the inner side.
Generally, a photocurable resin such as a UV-curing resin or the like is used in the aforementioned formation of the protective layer and adhering of the disks. At the time that light is irradiated onto the photocurable resin and the resin is photocured, when the light is irradiated at the same time onto the dye recording layer as well, there is the concern that the dye contained in the recording layer may partially decompose such that the recording characteristics deteriorate. However, conventional CD-Rs and DVD-Rs have a structure in which a layer for blocking light, such as a light reflecting layer, is provided between the layer to be photocured and the dye recording layer. Thus, light is not directly irradiated onto the dye recording layer, and the problem of deterioration in recording characteristics does not occur.
Due to the development of laser technology in recent years, short wavelength lasers such as blue lasers and the like have come to be put into practice. Accordingly, the development of novel optical information recording media, at which recording can be carried out at a high density by light of a wavelength of about 450 nm which is shorter than conventional recording wavelengths (of 780 nm or 630 nm), has progressed. Generally, the more the beam diameter of the irradiated laser light is made small, the more high density recording is possible. In order to decrease the beam diameter, the dye recording layer must be formed at a more shallow position from the surface. Thus, in an optical information recording medium for short wavelengths, a thin protective layer is provided at the side opposite a substrate of a predetermined thickness (1.2 mm in a CD-R), and recording is carried out by light being irradiated from the thin protective layer side.
However, when attempts are made to provide the thin protective layer at the side opposite the substrate, the light reflecting layer, the dye recording layer, and the thin protective layer are formed in that order on the substrate. When light is irradiated onto the photocurable resin and the resin photocures and the thin protective layer is formed, light is irradiated onto the dye recording layer as well at the same time. Namely, in the structure of an optical recording medium for short wavelengths, a problem arises in that, at the time of manufacture, the dye contained in the recording layer partially decomposes, and the recording characteristics deteriorate.
Further, in conventional CD-Rs and DVD-Rs, in order to prevent scratches from being formed in the substrate surface which is the surface on which the recording light and playback light are incident, the proposal has been made to provide a hard-coat layer, which is very hard and is formed from a photocurable resin, on the substrate surface. However, in this case as well, when light is irradiated onto the photocurable resin and the resin is photocured and the hard-coat layer is formed, light is irradiated onto the dye recording layer as well at the same time. Thus, a problem arises in that, at the time of manufacture, the dye contained in the recording layer partially decomposes, and the recording characteristics deteriorate.
The present invention was developed in light of the above-described drawbacks of the prior art, and an object of the present invention is to provide an optical information recording medium which has good recording characteristics by suppressing the decomposition of a dye contained in a dye recording layer at the time that a photocurable resin is photocured to form a photocured layer. Another object of the present invention is to provide a method of manufacturing an optical information recording medium in which a photocurable resin can be photocured and a photocured layer can be formed, without a dye contained in a dye recording layer decomposing.
The above-described objects are achieved by the following means.
A first aspect of the optical information recording medium of the present invention is an optical information recording medium comprising: a substrate; a recording layer on which information can be recorded by laser light, and which contains a dye having a main absorption band in a predetermined wavelength region; and a photocured layer which is formed by photocuring by light of a wavelength other than the predetermined wavelength region.
A second aspect of the optical information recording medium of the present invention is an optical information recording medium comprising: a transparent substrate; a recording layer which is formed on one surface of the transparent substrate, and on which information can be recorded by laser light, and which contains a dye having a main absorption band in a predetermined wavelength region; and a photocured layer which is formed on another surface of the transparent substrate, and which is formed by photocuring by light of a wavelength other than the predetermined wavelength region.
A third aspect of the optical information recording medium of the present invention is an optical information recording medium comprising: a substrate; a light reflecting layer which is formed on the substrate; a recording layer which is formed on the light reflecting layer, and on which information can be recorded by laser light, and which contains a dye having a main absorption band in a predetermined wavelength region; and a photocured layer which is formed on the recording layer by photocuring by light of a wavelength other than the predetermined wavelength region.
In the optical information recording media of the first through third aspects, the recording layer, on which information can be recorded by laser light, contains a dye having a main absorption band in a predetermined wavelength region. The photocured layer is formed by photocuring by light in a wavelength region other than the predetermined wavelength region in which the dye has the main absorption band. Thus, at the time of manufacturing, the decomposition of the dye contained in the dye recording layer is suppressed, and the optical information recording media have good recording characteristics.
Here, light in a wavelength region other than the predetermined wavelength region, i.e., light which is other than light in the main absorption band of the dye contained in the dye recording layer, is light in a wavelength region at which the light transmittance of the dye recording layer alone is at least 50% or more (0.3 or less as expressed by optical density). In order to better suppress decomposition of the dye, light in a wavelength region at which the light transmittance is 60% or more is preferable, and light in a wavelength region at which the light transmittance is 70% or more is more preferable.
Further, in order to better suppress the decomposition of the dye, the amount of irradiation of the photocurable resin by light in the wavelength region at which the light transmittance of the dye recording layer alone is at least 50% or more is preferably 50% or more, and more preferably 60% or more, and particularly preferably 70% or more, with respect to the entire amount of irradiation.
A fourth aspect of the optical information recording medium of the present invention is an optical information recording medium comprising: a substrate; a light reflecting layer which is formed on the substrate; a recording layer which is formed on the light reflecting layer, and on which information can be recorded by laser light, and which contains a dye having a main absorption band in a wavelength region of 400 nm or less; and a photocured layer which is formed on the recording layer by photocuring such that an amount of irradiation by light in a wavelength region of 400 nm or less is less than an amount of irradiation by light in a wavelength region at a longer wavelength side of 400 nm.
In the fourth aspect of the optical information recording medium of the present invention, the recording layer, on which information can be recorded by laser light, contains a dye having a main absorption band in the wavelength region of 400 nm or less. The photocured layer, which is formed on the recording layer, is formed by photocuring such that the amount of irradiation by light in the wavelength region of 400 nm or less, in which the dye has a main absorption band, is less than the amount of irradiation by light in the range of wavelengths longer than 400 nm. Thus, at the time of manufacturing, the decomposition of the dye contained in the dye recording layer is suppressed, and the optical information recording medium has good recording characteristics.
In the fourth aspect of the optical information recording medium of the present invention, in order to better suppress the decomposition of the dye, the amount of irradiation of the photocurable resin by light in the wavelength region of 400 nm or less is preferably 40% or less, and more preferably 30% or less, and even more preferably 20% or less, of the entire amount of irradiation (the amount of irradiation in the range of wavelengths of 300 to 800 nm).
A method of manufacturing an optical information recording medium of the present invention comprises the step of: manufacturing an optical information recording medium by forming, on a substrate on which is formed a recording layer on which information can be recorded by laser light and which contains a dye having a main absorption band in a predetermined wavelength region, a photocured layer by photocuring a photocurable resin by light of a wavelength other than the predetermined wavelength region.